EN 50126-2:2017 (E)
3
9
Specification of System Safety Requirements .............................................................. 32
9.1 General .............................................................................................................. 32
9.2 Safety requirements ........................................................................................... 32
9.3 Categorization of Safety Requirements ............................................................... 32
9.3.1 General .................................................................................................. 32
9.3.2 Functional safety requirements ............................................................... 33
9.3.3 Technical safety requirements ................................................................ 34
9.3.4 Contextual safety requirements ............................................................... 34
10 Apportionment of functional Safety Integrity requirements ............................................ 35
10.1 Deriving and apportioning system safety requirements ....................................... 35
10.2 Functional safety integrity for electronic systems ................................................ 35
10.2.1 Deriving functional safety requirements for electronic systems................ 35
10.2.2 Apportioning safety requirements ............................................................ 35
10.2.3 Safety Integrity Factors ........................................................................... 38
10.2.4 Functional safety integrity and random failures ....................................... 38
10.2.5 Systematic aspect of functional safety integrity ....................................... 38
10.2.6 Balanced requirements controlling random and systematic failures ......... 38
10.2.7 The SIL table .......................................................................................... 39
10.2.8 SIL allocation .......................................................................................... 40
10.2.9 Apportionment of TFFR after SIL allocation ............................................ 40
10.2.10 Demonstration of quantified targets ........................................................ 40
10.2.11 Requirements for Basic Integrity ............................................................. 41
10.2.12 Prevention of misuse of SILs .................................................................. 42
10.3 Safety Integrity for non-electronic systems – Application of CoP ......................... 42
11 Design and implementation .......................................................................................... 43
11.1 Introduction ........................................................................................................ 43
11.2 Causal analysis .................................................................................................. 43
11.3 Hazard identification (refinement) ....................................................................... 44
11.4 Common cause analysis ..................................................................................... 44
Annex A (informative) ALARP, GAME, MEM ..................................................................... 46
A.1 ALARP, GAME, MEM as methods to define risk acceptance criteria ............................ 46
A.2 ALARP (As Low As Reasonably Practicable) ............................................................... 47
A.2.1 General .............................................................................................................. 47
A.2.2 Tolerability and ALARP ....................................................................................... 48
A.3 Globalement Au Moins Equivalent (GAME) principle .................................................... 48
A.3.1 Principle ............................................................................................................. 48
A.3.2 Using GAME ....................................................................................................... 49
A.3.2.1 General .............................................................................................................. 49
A.3.2.2 Basic principles .................................................................................................. 49
A.3.2.3 Using GAME to construct a qualitative safety argument ...................................... 49
A.3.2.4 GAME using quantitative risk targets .................................................................. 49
A.4 Minimum Endogenous Mortality MEM .......................................................................... 50
Annex B (informative) Using failure and accident statistics to derive a THR ...................... 52
Annex C (informative) Guidance on SIL Allocation ............................................................ 53
Annex D (informative) Safety target apportionment methods ............................................. 55
D.1 Analysis of the system and methods ............................................................................ 55
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